The present invention relates to apparatus and methods used in oil well drilling and oil well operations for transmitting measurement data to a surface station from locations in a borehole.
Measurement While Drilling (MWD) and Logging While Drilling (LWD) systems derive much of their value from the ability to provide real-time information about conditions near the drill bit. Oil companies use these downhole measurements to make decisions during the drilling process, and sophisticated drilling techniques, such as the GeoSteering system developed by Schlumberger, Ltd. Such techniques rely heavily on instantaneous knowledge of the formation that is being drilled. The industry continues to develop new measurements for MWD/LWD, including imaging type measurements with high data content.
These new measurement and control systems require telemetry systems having higher data rates than those currently available. As a result, a number of telemetry techniques for use with measurement while drilling have been tried or proposed.
The industry standard is mud pulse telemetry that uses the drill pipe to guide acoustic waves in the drilling fluid. Currently, using mud pulse telemetry, data is sent to the surface at bit rates in the range of 1-6 bits/second. Such a slow rate is incapable of transmitting the large amounts of data that are typically gathered with an LWD string. In some cases (e.g., foamed drilling fluid), mud pulse telemetry does not work at all. Normally, some or all of the data is stored in downhole memory and downloaded at the end of the bit run. This delay significantly reduces the value of the data for real-time applications. Also, there is a significant risk of data loss, for example, if the tool is lost in the hole.
Electromagnetic telemetry via earth path has been tried with limited success. Even at very low data rates, it works only to a limited depth, depending on the resistivity of the earth.
Acoustic telemetry through the drill pipe itself has been studied extensively but not used commercially, so far. In theory, data rates in the 10""s of bits/second should be possible using acoustic waves in the steel.
The idea of putting a wire in the drill pipe has been proposed numerous times over the past 25 years. Shell and Exxon each reportedly built an experimental wired drill string in the late 1970""s. Prior art relating to these efforts is disclosed in U.S. Pat. No. 4,126,848 to Denison, xe2x80x9cDrill String Telemeter Systemxe2x80x9d; U.S. Pat. No. 3,957,118 to Barry et al., xe2x80x9cCable System for use in a Pipe String and Method for Installing and Using the samexe2x80x9d; and U.S. Pat. No. 3,807,502 to Heilhecker et al., xe2x80x9cMethod for Installing an Electric Conductor in a Drill Stringxe2x80x9d; and the publication xe2x80x9cFour Different Systems Used for MWDxe2x80x9d, W. J. McDonald, The Oil and Gas Journal, pages 115-124, Apr. 3, 1978. Such systems are believed to have suffered from poor reliability and high cost because of the large number of electrical connectors.
IFP developed a system known as xe2x80x9cSimphorxe2x80x9d which used wireline cables and large, robust wet connectors. It has never been commercialized for measurement while drilling applications. This system is believed to have suffered from interference with the drilling process.
The use of current-coupled inductive couplers in drill pipe is known. U.S. Pat. No. 4,605,268, to Meador, xe2x80x9cTransformer cable connectorxe2x80x9d describes the use and basic operation of current-coupled inductive couplers mounted at the sealing faces of drill pipes. Russian Federation published patent application 2140527, xe2x80x9cA method for drilling oblique and horizontal boreholesxe2x80x9d, filed Dec. 18, 1997, and an earlier Russian Federation published patent application 2040691, xe2x80x9cA system for transmitting electrical energy and data within a column of adjoining tubesxe2x80x9d, filed Feb. 14, 1992, both describe a drill pipe telemetry system that uses current-coupled inductive couplers mounted proximate to the sealing faces of drill pipes. WO Publication 90/14497A2, by Eastman Christensen GMBH, xe2x80x9cProcess and device for transmitting data signals and/or control signals in a pipe trainxe2x80x9d describes an inductive coupler mounted at the ID of the drill pipe joint for data transfer.
Other US patents are as follows: U.S. Pat. No. 5,052,941 to Hernandez-Marti et al., xe2x80x9cInductive coupling connector for a well head equipmentxe2x80x9d; U.S. Pat. No. 4,806,928 to Veneruso, xe2x80x9cApparatus for electro-magnetically coupling power and data signals between well bore apparatus and the surfacexe2x80x9d; U.S. Pat. No. 4,901,069 to Veneruso, xe2x80x9cApparatus for electro-magnetically coupling power and data signals between a first unit and a second unit and in particular between well bore apparatus and the surfacexe2x80x9d; U.S. Pat. No. 5,531,592 to Veneruso; xe2x80x9cMethod and apparatus for transmitting information relating to the operation of a downhole electrical devicexe2x80x9d; U.S. Pat. No. 5,278,550 to Rhein-Knudsen, et al., xe2x80x9cApparatus and method for retrieving and/or communicating with downhole equipmentxe2x80x9d; and U.S. Pat. No. 5,971,072 to Huber et al., xe2x80x9cInductive coupler activated completion systemxe2x80x9d.
None of these references has provided a telemetry system for reliably transmitting measurement data at high data rates from locations near the drill bit to a surface station. Therefore, there exists a need for a telemetry system for reliably transmitting measurement data at high data rates to a surface station from locations in a borehole.
The present invention provides a robust, low-loss wired pipe joint for service as a component of a wired pipe string for transmitting measurement data to a surface station from locations in a borehole in oil well drilling and oil well operations. Conductive layers reduce signal energy losses over the length of the drill string by reducing resistive losses and flux losses at each inductive coupler. The wired pipe joint is robust in that it remains operational in the presence of gaps in the conductive layer.
A wired pipe joint in accordance with the present invention includes an elongate tubular shank having an axial bore, a threaded box-end, and a threaded pin end. A first annular coil, fixedly mounted to the box-end is partially surrounded by a first high-conductivity, low-permeability layer, and a second annular coil fixedly mounted to the pin-end is partially surrounded by a second high-conductivity, low-permeability layer, such that when the box-end of a first wired pipe joint is coupled for operation with the pin-end of a second wired pipe joint, the first and second high-conductivity, low-permeability layers form at least a portion of a toroidal path enclosing the first annular coil of the first wired pipe joint and the second annular coil of the second wired pipe joint. Coil windings of the first and second coils of the wired pipe joint are electrically coupled.
An inductive coupler in accordance with the present invention includes a threaded box-end with a first annular coil fixedly mounted thereto and a first high-conductivity, low-permeability layer partially surrounding the first annular coil. It further includes a threaded pin-end with a second annular coil fixedly mounted thereto and a second high-conductivity, low-permeability layer partially surrounding the second annular coil. A first electrical terminal is coupled to a first coil winding of the first annular coil, and a second electrical terminal is coupled to a second coil winding of the second annular coil. The threaded box-end, the threaded pin-end, and the two layers are structured such that when the threaded box-end is coupled for operation with the threaded pin-end, the first and second layers form at least a portion of a toroidal path enclosing the first and second annular coils.
A first preferred embodiment is shown in FIG. 1. FIG. 1 shows wired pipe joint including an elongate tubular shank having an axial bore, a first inductive coupler element at a box-end, and a second inductive coupler element at a pin-end. An inductive coupler is shown as constituted by a first inductive coupler element and a second inductive coupler element of the pin-end of an adjacent wired pipe string. The box-end defines an internal thread and an annular inner shoulder with a first slot. The first slot defines a first annular concave surface with concentric facing portions. The first annular concave surface has a first annular concave high-conductivity, low-permeability layer thereon. The box-end includes a first coil located between concentric facing portions of the first high-conductivity, low-permeability layer. The pin-end defines an external thread and an annular inner contacting pipe end with a second slot. The second slot defines a second annular concave surface with concentric facing portions. The second annular concave surface has a second annular concave high-conductivity, low-permeability layer thereon. The pin-end includes a second coil located between concentric facing portions of the second high-conductivity, low-permeability layer.
The first high-conductivity, low-permeability layer constitutes a first high-conductivity, low-permeability shaped belt that partially encloses the first coil. It is shaped to cooperate with the second high-conductivity, low-permeability shaped belt of an adjacent second pipe joint having a second coil and a second high-conductivity, low-permeability shaped belt to create a closed high-conductivity, low-permeability toroidal path. This closed path encloses the first coil and the second coil when the first and second pipe joints are locked together as part of an operational pipe string.
The first preferred embodiment includes a dual-contact pipe joint with first and second inductive coupler elements located at an inner shoulder and an inner pipe end, respectively. The dimensions of the pipe joint are such that the distance between the outer pipe end and the inner shoulder, is greater than the distance between the outer shoulder and the inner pipe end, by a small amount. When two pipe joints are properly tightened (i.e. forced together with the torque needed to achieve proper pipe-sealing of an outer end against an outer shoulder of an adjacent wired pipe), this small amount allows that same torque to automatically tighten the inner shoulder against the inner pipe end of an adjacent wired pipe joint so as to reliably form a closed high-conductivity, low-permeability toroidal path.